A number of prior proposals have been made for manufacturing a composite core panel formed from a honeycomb panel formed with tubular cells at right angles to the panel where the panel is filled with a reinforcing foam extending through the cells so as to provide an enhanced compression strength of the core in a direction longitudinally of the cells. This strength is commonly significantly greater than the compression strength of the core and the foam separately. The core panel is then covered on top and bottom by reinforcing sheets of a fibrous reinforcing material which are then resin filled by a resin impregnation process, for example infusion, so as to attach the top and bottom sheets to the foam and honeycomb core panel. The compression strength of the core panel has a direct relationship to the shear strength of the finished panel so that it has been desirable to maximize this compression strength. Such panels have become widely used for many products
The materials commonly used for the honeycomb panel are phenolic paper, aluminum and various types of plastic materials. The selection is made in part dependant on cost relative to the desired strength with the aluminum of course providing the highest strength at the highest cost. Phenolic paper is the simplest and cheapest option and is very widely used. The honeycomb, in many cases, is formed by bonding strips side by side with the tubular cells formed around rods or simply by stretching the bonded strips longitudinally of the panel to open them up. Adhesive and heat sealing can be used for attaching the strips.
However there is always an ongoing requirement for yet further increasing the strength of such panels to enable additional markets to be entered or for strength requirements to be met with a thinner panel of less material.